Atomizing nozzle

ABSTRACT

Atomizing nozzle for introducing a gas/liquid mixture into a chemical reformer to produce hydrogen, having at least one gas supply line ( 21 ) for a gas stream ( 20 ), at least one liquid supply line ( 25, 27 ) and at least one outlet ( 19 ) for the atomized gas/liquid mixture as well as a first chamber ( 24 ) into which the liquid supply line ( 25, 27 ) empties, with the chamber ( 24 ) having a chamber wall ( 16 ) that forms a lip ( 18 ) at the outlet end, on both sides of which a separate gas flow ( 20, 22 ) is supplied.

[0001] The present invention relates to an atomizing nozzle, in particular for introducing a gas/liquid mixture into a chemical reformer according to the definition of the species in claim 1.

BACKGROUND INFORMATION

[0002] Among the alternative drive concepts for motor vehicles, fuel cell-supported systems, in particular, are currently generating a great deal of attention. These systems typically include PEM (polymer electrolyte membrane) fuel cells that operate with hydrogen and air as the energy carriers.

[0003] Because hydrogen refueling and storage in the motor vehicle remains a problem, hydrogen is produced directly on-board as needed in an upstream reformer stage from easy-to-handle fuels such as methanol, methane, diesel oil or gasoline and consumed immediately. The reformers employed for this purpose are chemical reactors that are used to partially oxidize the fuels by adding air and moisture, for example at a temperature of 800° C., in catalytic converters, producing hydrogen and other secondary products, such as CO and CO₂.

[0004] Supplying the reformer with the educts needed for the reaction is thus a very important step. All educts, such as air, water and fuel, are typically supplied to the reformer in a gaseous state. This requires an evaporation tube that is able to provide the proper amounts of gaseous fuel and steam.

[0005] However, problems arise during the cold start phase, since the liquid educts cannot be vaporized by the reformer waste heat, but only by an electrically heated evaporator. In addition, conventional evaporators are unable to instantaneously generate the proper quantities of gaseous reactants when load change requirements vary abruptly.

[0006] Alternative concepts have thus been developed to inject fuels and water directly into the reformer in liquid form. However, to carry out the reaction in the reformer as efficiently as possible, the liquid educts must be introduced into the reformer in a finely dispersed form. A reactor for producing hydrogen that has a nozzle for injecting liquid hydrocarbons into an air stream is known from U.S. Pat. No. 3,971,847. The resulting mist is swirled on baffle plates before entering the actual reaction zone. However, the water needed for the reaction is evaporated separately in an evaporation tube.

[0007] The object of the present invention is to provide an atomizing nozzle for the simultaneous atomization of water and liquid fuels, with the atomizing nozzle having a very high degree of educt atomization and mixing and, in addition, being designed for instantaneous metering of liquid educts.

ADVANTAGES OF THE INVENTION

[0008] The atomizing nozzle according to the present invention having the characterizing features of claim 1 has the advantage that a gas/liquid mixture is generated which is distinguished by a high degree of atomization and thorough reactant mixing. It also gives the system a good cold start performance and provides adequate response to dynamic load changes.

[0009] The high degree of atomization is achieved by conducting the liquid to be atomized into a chamber through which a gas stream flows and by having the liquid film forming on the chamber wall surrounded and entrained by the gas stream at a lip or separating edge. A particularly advantageous feature is that a gas flow passes around both sides of the lip at high speed, which further enhances the atomizing effect and produces very large spray angles. This is necessary if the reformer is to have a compact design. Because the atomizing nozzle includes multiple liquid and gas supply lines, the necessary mixture quantity and composition may be provided in each case, depending on the reformer operating state.

[0010] Because the liquid atomization process is exclusively gas-supported, only low liquid pressures are necessary and there is no need to install expensive high-pressure pumps.

[0011] Advantageous embodiments and refinements of the present invention are made possible by the features described in the subordinate claims. Thus, the atomizing nozzle is advantageously provided with an annular lip and an outlet and includes an axially moving plunger which maintains a uniformly high gas flow rate despite varying gas volume flows at the lip. The plunger has at least one further liquid supply line that ensures the pressure-supported metering of liquid educts directly into the reformer. This is useful, especially when the system has low load requirements, because the low gas volume flows in this case do not enable adequate gas-supported atomization of the liquid reactants. Direct pressure-supported injection of the liquid educts is also advantageous when the load requirements rise abruptly, since the additional quantity of liquid educts needed may be provided without delay.

[0012] In a particularly advantageous embodiment, two separate gas supply lines are provided, each of which empties into a separate chamber within the atomizing nozzle. Both chambers are arranged so that they share a common wall whose outlet end forms the lip. This makes it possible to expose the lip to two gas flows of different speeds and compositions.

[0013] According to an advantageous embodiment, gas guiding devices are provided in at least one of the chambers for the purpose of swirling the gas flow. This increases the mixing degree of the gas/fluid mixture.

[0014] It is further advantageous to design the chamber and plunger surfaces so that the chamber cross-section between the chamber wall and plunger has a minimum in the lip area, and the resulting high gas flow rates produce effective atomization of the liquid.

DRAWINGS

[0015] An exemplary embodiment of the present invention is illustrated in the drawing and explained in greater detail in the following description.

[0016] The FIGURE shows a cross-section of the atomizing nozzle according to the present invention.

EXEMPLARY EMBODIMENT

[0017]FIG. 1 shows a cross section of atomizing nozzle 10 according to the present invention, which is provided in a reactor wall of a partially illustrated chemical reformer 12.

[0018] Atomizing nozzle 10 includes a housing 14 which has an outlet 19 on the reactor side. Outlet 19 is designed, for example, with an annular shape. A first chamber 24, into which at least one first gas supply line 21 which supplies a first gas flow 20 to chamber 24 empties, is located in housing 14. A first liquid supply line 25 and a second liquid supply line 27, which supply liquid educts to chamber 24, are provided downstream and empty into first chamber 24. To prevent subsequent liquid leakage, liquid supply lines 25, 27 are equipped with spring-loaded non-return valves 29.

[0019] Annular gaps 28, 30, which enable the outflowing liquid to wet entire wall 16 of chamber 24, are provided at the outlets of liquid supply lines 25, 27. Wall 16 of chamber 24, which is covered by the liquid film, is delimited on the outlet side by a lip 18 at which the liquid film is entrained and atomized. Chamber 24 may also have a means (not illustrated) for swirling the gas flow, such as a gas guiding device.

[0020] A plunger 32, whose surface 34 matches the geometry of chamber wall 16, is also provided inside chamber 24, with the distance between plunger surface 34 and chamber wall 16 having a minimum in the area of lip 18. This produces high flow velocities in the area of lip 18, thus effectively atomizing the liquid. It is especially advantageous for the surfaces of plunger 34 and chamber 16 to approach each other in the area of lip 18 in a manner that forms a venturi tube-like passage, since this minimizes any throttle losses that occur and optimizes the mixing of gas and atomized liquid.

[0021] Plunger 32 includes in the axial direction at least one, preferably two, additional liquid supply lines 35 that ensure direct pressure-supported metering of liquid educts into the reformer. For this purpose, an atomizer 36 that is designed, for example, as a swirl nozzle or a perforated jet nozzle having one or more holes is provided at the outlet end of further liquid supply line 35. The pressure supported metering of liquid educts is especially important in the case of low system load requirements, when adequate atomization is not possible due to the low volume of gas to be supplied. Direct pressure-supported injection of the liquid educts is also advantageous when the system load requirements increase abruptly, since the additional quantity of liquid educts needed may be provided without delay.

[0022] Plunger 32 is attached to housing 14 by extension or compression springs 33 so that the spring resistance of springs 33 compensates for the forces applied by the gas flow onto plunger 32 in the axial direction and, due to the small cross-section of chamber 24, produces a high velocity of gas flow 20. This reduces the gap width between chamber wall 16 and the surface of plunger 34, corresponding to a weak gas flow 20, when the load requirements are low and increases the gap width when the load requirements are high. This makes it possible to adjust the gap width to the throughput. FIG. 1 shows an arrangement in which plunger 32 is attached to a shoulder 37 by an extension spring 33.

[0023] In addition to first chamber 24, a second chamber 26 into which empties at least one second gas supply line 23 supplying a second gas flow 22 to chamber 26 is also provided in housing 14. Chamber 26 and chamber 24 share a common wall 15 whose thickness diminishes on the outlet side and forms lip 18. Chamber 26 is thus preferably designed so that its chamber wall forms a venturi tube-like passage for gas flow 22 in the area of the lip. Chamber 26 is arranged around chamber 24, for example in the form of a cylindrical surface.

[0024] All components of atomizing nozzle 10 are made, for example, of stainless steel, although other heat- and corrosion-resistant materials may also be used.

[0025] A number of different educt mixtures may be used to produce hydrogen, depending on the requirements. Thus, hydrogen is obtainable by partially oxidizing fuels and adding either steam, air or a mixture of both. Conversion takes place in a catalytic converter that is heatable by the usual methods, using gasoline, diesel, methane, or methanol as fuels. Methanol/water mixtures or fuel/water emulsions are also suitable.

[0026] The reformer and the overall system have different operating states, depending on the fuel cell load requirements. The atomizing nozzle according to the present invention is also always able to provide the system with the necessary educts in the required quantities and composition even when the operating states vary.

[0027] Under steady-state operating conditions, air and/or steam must be supplied to the reformer. This may be done either by supplying steam to the reformer, for example via gas supply line 23, and air via gas supply line 21, or by supplying both gas supply lines 21, 23 with an air/steam mixture. It is thus possible to supply air and steam to the reformer either in premixed form or as largely separate gas flows. The liquid fuel is preferably supplied via first or second liquid supply line 25, 27 and enters reformer 12 in a finely dispersed form. A possible alternative is to inject the fuel directly into the reformer via further liquid supply line 35. Alternatively, water may also be supplied to the system via liquid supply lines 35, 27, 35. This is especially useful in the case of abrupt load changes.

[0028] During the system cold start phase, steam is unavailable, and water is supplied to the reformer in liquid form. The high atomization degree of the gas/liquid mixtures produced by the atomizing nozzle according to the present invention significantly accelerates starting. In addition, starting performance may be further improved by a heated catalytic converter in the reformer.

[0029] If the atomizing nozzle is coupled with a corresponding metering system for the gaseous and liquid educts, the metering and atomizing functions are advantageously physically separated from each other. This is especially important, since the metering valves require expensive cooling when positioned near the reformer.

[0030] The atomizing nozzle according to the present invention is not limited to the exemplary embodiment described above, but instead further embodiments of an atomizing nozzle based on gas flow-supported atomization are conceivable. For example, it is not absolutely necessary to integrate the atomizing nozzle into the reactor wall of reformer 12, but instead it may be positioned in the reformer supply line system. 

1. An atomizing nozzle for a gas/liquid mixture, in particular for introduction into a chemical reformer to produce hydrogen, having at least one gas supply line for a gas stream, at least one liquid supply line, and at least one outlet for the atomized gas/liquid mixture, as well as a first chamber into which the liquid supply line empties, with the first chamber having a chamber wall that forms a lip at the outlet end, on either side of which a gas stream is supplied, wherein at least one first liquid supply line (25) and at least one second liquid supply line (27) are provided.
 2. The atomizing nozzle according to claim 1, wherein a first gas supply line (21) is provided which leads to the first chamber (24) upstream from the outlet of the liquid supply line (23); a second gas supply line (23) leads to a second chamber (26); and both chambers (24, 26) share a common wall (15) which forms the lip (18) at its outlet end.
 3. The atomizing nozzle according to claim 1 or 2, wherein the lip (18) and/or the outlet (19) have an annular shape.
 4. The atomizing nozzle according to claims 1 through 3, wherein the first and second liquid supply lines (25, 27) each empty into a separate annular gap (28, 30) within the chamber (24).
 5. The atomizing nozzle according to one of claims 1 through 4, wherein spring-loaded non-return valves (29) are provided in the liquid supply lines (25, 27) to prevent subsequent fluid leakage.
 6. The atomizing nozzle according to at least one of claims 1 through 5, wherein the liquid includes water and/or a fuel.
 7. The atomizing nozzle according to claim 1, wherein the chamber (24) has at least one means for swirling the gas stream (20).
 8. The atomizing nozzle according to claim 1, wherein the gas stream (20, 22) includes air and/or steam.
 9. The atomizing nozzle according to at least one of the preceding claims, wherein an axially moving plunger (32) whose surface (34) has a geometry that at least approximately matches that of the wall (16) of the chamber (24) is provided in the first chamber (24); and the plunger (32) is attached to the housing (14) by at least one spring (33).
 10. The atomizing nozzle according to claim 9, wherein the cross-section of the plunger (32) increases in size at the outlet end so that the distance from its surface (34) to the chamber wall (16) has a minimum in the area of the lip (18).
 11. The atomizing nozzle according to claim 9 and 10, wherein the plunger (32) is in the form of a stamp and includes at least one further liquid supply line (35) which has a further nozzle (36) on the end face of the plunger (32) for the pressure-supported atomization of the supplied liquid.
 12. Use of the atomizing nozzle according to at least one of claims 1 through 11 for atomizing liquid educts in a reformer for fuel cells. 